1. Field of the Invention
This invention relates generally to magnetic recording heads, particularly to perpendicular recording heads that produce recording magnetic fields that are substantially perpendicular to the recording medium. More specifically, the invention relates to a tapered shape of a magnetic pole of a recording head that allows a more efficient delivery of a magnetic recording field to a recording medium.
2. Description of the Related Art
The increasing need for high recording area densities (up to 500 Gb/in2) is making the perpendicular magnetic recording head (PMR head) a replacement of choice for the longitudinal magnetic recording head (LMR head).
By means of fringing magnetic fields that extend between two emerging pole pieces, longitudinal recording heads form small magnetic domains within the surface plane of the magnetic medium (hard disk). As recorded area densities increase, these domains must correspondingly decrease in size, eventually permitting destabilizing thermal effects to become stronger than the magnetic interactions that tend to stabilize the domain formations. This occurrence is the so-called superparamagnetic limit.
Recording media that accept perpendicular magnetic recording, allow domain structures within a magnetic layer to be formed with a perpendicular orientation relative to the disk surface, while a soft magnetic underlayer (SUL) formed beneath the magnetic layer acts as a stabilizing influence on these perpendicular domain structures and also serves to channel a return flux back to the head to strengthen the recording field. Thus, a magnetic recording head that produces a field capable of forming domains perpendicular to a disk surface, when used in conjunction with such perpendicular recording media, is able to produce a stable recording with a much higher area density than is possible using standard longitudinal recording.
Although the magnetic media used in conjunction with perpendicular writing are capable of storing a high area density, the write head itself must be able to produce magnetic fields of sufficient intensity and definition to make use of the media's capabilities. One approach to matching the writer capabilities to those of the media is to fabricate a tapered magnetic pole tip. Such a design presents a smaller footprint where it emerges at the ABS, yet delivers more flux. U.S. Pat. No. 7,322,095 and U.S. Patent Applications 2008/0112082 and 2005/0237665 (Guan et al.) show such a main pole tapered preferably at its trailing edge and shielded on four sides.
Traditionally, a top yoke (TY), a bottom yoke (BY) or both have been used in PMR writers to deliver flux to the main pole. As a consequence, these yokes are often referred to as auxiliary poles. Referring to FIGS. 1a-1b, there are shown the following prior art arrangements.
FIG. 1a shows a highly schematic diagram of a side view of a PMR single pole (14) writer positioned above a moving magnetic media (16). The media is moving in the direction of the arrow (180). The term “leading edge” (indicated in the figure by the legend “Leading Edge”) of the writer or its various elements refers to the edge or surface into which the disk is moving. Typically, the read head, which is not shown here, would be formed on the leading edge side of the writer, so an area on the disk moves past the reader before passing beneath the writer. Where a figure does not indicate a disk or a reader, the notation of leading or trailing will be indicated by a legend. For consistency of description, a set of x, y, z axes define directions in this and remaining figures that display a PMR writer. The positive y-direction is away from the ABS of the writer. The x-direction defines the thickness direction of the pole layer (14) and the yoke layer (17) (i.e. the direction of layer formation by plating or the like). The positive z-direction (circle with a central dot) is out of the figure plane.
The main pole of this writer (14) consists of flared portion (11), which will be more clearly shown in FIG. 1b, and a narrow pole tip (13), which extends from the flared portion and presents an exposed ABS shape (19) just above the media (16). The writer has a return pole (15), that completes a magnetic flux loop (not shown), out from the main pole, through the media soft underlayer, back up through the return pole (15) and around through a bottom yoke (17) (formed beneath the pole) to which the pole tip is attached. A single exemplary current carrying coil winding (12) is shown as wrapped around the yoke (17) and represents the mechanism by which a magnetic field is generated. The ABS surface of the writer is indicated by the dashed line with the legend “ABS”. The main pole (14), in this configuration, is mounted on the leading edge surface of the bottom yoke (17).
Referring next to FIG. 1b there is shown, schematically, a top view of the main pole (14) and pole tip (13), as it would appear if viewed along the thickness direction of the writer, or the arrow (180), or the x-axis of FIG. 1a. Note, as discussed above, that the main pole (14) generally has a horizontal shape that includes a small rectangular portion (13) and a triangular flaring portion (11). The pole tip projects from the narrow portion of (1). The ABS surface (19) of the pole tip (13) has a width, w, and the pole tip itself has neck height NH, defined by its length before the taper if the pole tip is reached.
Referring now to FIGS. 2a, 2b and 2c, there are shown three possible approaches to channeling magnetic flux from a yoke to a main pole, any of which could be applied to the configuration of FIG. 1a. In FIG. 2a, there is schematically shown the main pole (14) attached beneath the yoke (17a), which thereby acts as a top yoke. Typically, the distance, d, between the perpendicular edge of the yoke (18a) and the tip of the pole (19) is approximately 1.5 microns or greater.
In FIG. 2b, there is schematically shown the same main pole (14), with the yoke (17b) now serving as a bottom yoke and the same approximate 1.5 micron or greater distance between the yoke edge (18b) and the pole tip.
In FIG. 2c, there is shown a main pole configuration in which the main pole is sandwiched between a top (17a) and bottom (17b) yoke.
Referring finally to FIG. 2d, there is shown a top view of the configuration in FIG. 2c, in which the main pole (14) is shown projecting from between the top and bottom yokes (17a)/(17b). Note, this figure would appear substantially the same if it were used to illustrate the configurations of FIG. 2a or 2b, the difference being that only one yoke (17a) or (17b) would be seen.
Along with the above cited methods of attaching a pole tip to a top yoke, a bottom yoke or both, the tip itself may be provided with a tapering profile just above its emergence at the ABS of the writer. Referring to FIGS. 3a, 3b and 3c, there are shown three pole tips with trailing edge, leading edge and both leading and trailing edge, tapers. Note that a trailing (leading) taper refers to a bevel (reduction in thickness) that begins at the trailing (leading) edge face of the pole tip, a distance away from the ABS (shown as a dashed line) and produces a diminishing thickness towards the ABS face of the pole tip, at which point the bevel stops.
The methods by which the pole tip is tapered and the general design of the taper are also taught in the following patents and published applications.
U.S. Patent Application 2005/0219743 (Guan et al—Headway) discloses that the main pole may be tapered at the leading or the trailing edge.
U.S. Pat. No. 7,133,252 (Takano et al) shows that the main pole may be tapered at the leading edge or the trailing edge or both.
U.S. Pat. No. 5,600,519 (Heim et al) discloses a tapered pole tip.
U.S. Patent Application 2008/0316653 (Sasaki et al). FIG. 12 shows the pole tapered and the nonmagnetic layer 17 also tapered.